1. Technical Field
The present invention relates generally to the electronics field. More specifically, this invention relates to plug assemblies for use with electrical equipment to connect a cable from an electrical apparatus to another apparatus.
2. Description Of The Related Art
Electrical plug assemblies are in common use with a variety of electrical equipment, including equipment utilized in sensing or gathering data, such as an electrocardiograph, in which the plug is connected to an electrode probe, which in turn is secured to the chest of a patient to gather heartbeat data for producing an electrocardiogram. Such plug assemblies generally comprise an elongate, electrically conductive tip at one end of the plug assembly. The opposite end of the plug assembly is connected to an electrical cable. The intermediate portion of the plug assembly forms a handle for manipulation of the plug assembly.
In addition to its function as a plug, the plug assembly must protect the often delicate connection between the electrical cable and the electrically conductive tip. This connection may comprise a crimp or a solder joint; in either case, the connection is subject to failure if exposed to repeated bending and torsional loads applied in operation. Thus, the plug assembly should possess sufficient rigidity to protect the connection from failure due to bending and torsional loads. This function becomes even more important if an impedance-matching resistor or other electrical circuitry is provided between the cable and tip because the circuitry necessitates additional delicate connection points and separate electrical elements, all of which are subject to failure. However, the plug assembly cannot be wholly rigid, or else it will induce excessive strain at the juncture between the plug assembly and the electrical cable. This strain can cause electrical shorts or opens resulting in a premature failure of the electrical cable.
United Kingdom Patent Application No 2,170,058, published Jul. 23, 1986, discloses an electrical connector having one end adapted for connection to a thermocouple and an opposing end connected to a semi-rigid electrical cable. The connector includes concentric inner and outer tubes, the inner tube being coupled to the cable and the outer tube forming the housing of the connector. The inner and outer tubes are rotatable relative to one another to permit the connector to be rotated relative to the semi-rigid electrical cable so that the connector can be oriented independently of the semi-rigid cable for installations in which the final orientation of the connector relative to the thermocouple is uncertain. This disclosure demonstrates the difficulty in achieving the appropriate compromise between a rigid electrical connector and one that is sufficiently flexible to permit the connector or plug to be used in a variety of orientations without inducing undue strain on the cable to which it is attached. Because this disclosure is directed to use with semi-rigid cables, no strain relief means is provided, presumably because the semi-rigid cables are not subject to failure due to strain encountered in operation, as is the case with electrical cables connected to electrical plug assemblies, particularly those employed in conjunction with an electrocardiograph probe, in which the plug assembly and cable may be subjected to a relatively great amount of handling and manipulation during their operational lives.
A need exists, therefore, for an electrical plug assembly possessing sufficient rigidity to protect the electrical connections between the electrical cable and the electrically conductive tip from failure such as from bending, tension, and torsional loads, while simultaneously possessing sufficient flexibility and strain relief capability to prevent failure of the flexible electrical cable such as from strains encountered in operation. The electrical plug assembly should also be manufactured easily at low cost.